Magnetic resonance imaging apparatus and RF coil unit

Abstract

According to one embodiment, a magnetic resonance imaging apparatus includes a correction data acquisition unit configured to perform diffusion weighted imaging to a phantom having a known apparent diffusion coefficient and measure an apparent diffusion coefficient of the phantom to acquire correction data from a measured apparent diffusion coefficient and the known apparent diffusion coefficient, and an image generating unit configured to perform diffusion weighted imaging to an object with a same parameter setting as that of the diffusion weighted imaging to the phantom to generate an apparent diffusion coefficient image from a diffusion weighted imaging data of the object and the correction data.

1. A magnetic resonance imaging apparatus comprising:
 a correction data acquisition unit configured to perform diffusion weighted imaging to a phantom having a known apparent diffusion coefficient and measure an apparent diffusion coefficient of the phantom to acquire correction data from a measured apparent diffusion coefficient and the known apparent diffusion coefficient; and 
 an image generating unit configured to perform diffusion weighted imaging to an object with a same parameter setting as that of the diffusion weighted imaging to the phantom to generate an apparent diffusion coefficient image from a diffusion weighted imaging data of the object and the correction data. 
 
     
     
       2. The magnetic resonance imaging system according to  claim 1 , wherein,
 said image generating unit further generates fractional anisotropy image from the diffusion weighted imaging data and the correction data. 
 
     
     
       3. The magnetic resonance imaging system according to  claim 1 , wherein,
 the phantom has the substantially same size as an imaging region of the object, and 
 said correction data acquisition unit performs the diffusion weighted imaging to the phantom independently of the diffusion weighted imaging to the object, and acquires the correction data. 
 
     
     
       4. The magnetic resonance imaging system according to  claim 3 , wherein,
 the phantom has a known apparent diffusion coefficient having a spatially uniform distribution, 
 said correction data acquisition unit acquires the correction data which corrects an error depending on spatial positions of the imaging region, using an error between a spatial distribution of the measured apparent diffusion coefficient of the phantom and the spatially uniform distribution of the known apparent diffusion coefficient of the phantom unit, and 
 said image generating unit generates the apparent diffusion coefficient image of the object depending on the spatial positions, by using the correction data. 
 
     
     
       5. The magnetic resonance imaging system according to  claim 1 , wherein,
 the phantom is arranged in the circumference of the object, and 
 said correction data acquisition unit performs the diffusion weighted imaging to the phantom simultaneously with the object, and acquires the correction data. 
 
     
     
       6. The magnetic resonance imaging system according to  claim 1 , wherein,
 the phantom is configured to have a plurality of phantom units arranged in different positions in the circumference of the object, and 
 said correction data acquisition unit performs the diffusion weighted imaging to the phantom simultaneously with the object, and acquires the correction data. 
 
     
     
       7. The magnetic resonance imaging system according to  claim 6 , wherein,
 each of the phantom units has the known apparent diffusion coefficient of the same value, 
 said correction data acquisition unit acquires the correction data which corrects an error depending on spatial positions of the imaging region, the error having zeroth or first degree distribution function, using an error between the measured apparent diffusion coefficient of each of the phantom units and the known apparent diffusion coefficient of each of the phantom units, and 
 said image generating unit generates the apparent diffusion coefficient image of the object which is corrected depending on the spatial positions, by using the correction data. 
 
     
     
       8. The magnetic resonance imaging system according to  claim 6 , wherein,
 each of the phantom units has a known apparent diffusion coefficient of a value different from each other, 
 said correction data acquisition unit acquires the correction data which corrects an error depending on a magnitude of the apparent diffusion coefficient, using an error between the measured apparent diffusion coefficient of each of the phantom units and the known apparent diffusion coefficient of each of the phantom units, and 
 said image generating unit generates the apparent diffusion coefficient image of the object which is corrected depending on the magnitude of the apparent diffusion coefficient, by using the correction data. 
 
     
     
       9. The magnetic resonance imaging system according to  claim 8 , wherein,
 the error depending on the magnitude of the apparent diffusion coefficient is an error resulting from a nonlinear relation between a current value applied to a gradient coil and a magnitude of a gradient magnetic field. 
 
     
     
       10. The magnetic resonance imaging system according to  claim 6 , wherein,
 each of the phantom units is configured to have a plurality of subphantom units, each of the subphantom units having a known apparent diffusion coefficient of a value different from each other and being arranged close to each other, 
 said correction data acquisition unit acquires the correction data which corrects an error depending on spatial positions of the imaging region, the error having zeroth or first degree distribution function, using an error between the measured apparent diffusion coefficient of each of the phantom units and the known apparent diffusion coefficient of each of the phantom units, and corrects an error depending on a magnitude of the apparent diffusion coefficient, using an error between the measured apparent diffusion coefficient of each of the subphantom units and the known apparent diffusion coefficient of each of the subphantom units, and 
 said image generating unit generates the apparent diffusion coefficient image of the object which is corrected depending on the spatial positions and the magnitude of the apparent diffusion coefficient, by using the correction data. 
 
     
     
       11. The magnetic resonance imaging system according to  claim 1 , wherein,
 the phantom is configured to have a plurality of first phantoms arranged in different positions in the circumference of the object, and a second phantom which has a substantially same size as an imaging region of the object and has an apparent diffusion coefficient having a spatially uniform distribution, 
 said correction data acquisition unit performs a first diffusion weighted imaging to the first phantoms simultaneously with the object to acquire a first correction data, and performs a second diffusion weighted imaging to the second phantom independently of the first diffusion weighted imaging to the object to acquire a second correction data, and 
 the image generating unit generates the apparent diffusion coefficient image of the object from a diffusion weighted imaging data of the object acquired with the first diffusion weighted imaging, and the first and the second correction data. 
 
     
     
       12. The magnetic resonance imaging system according to  claim 11 , wherein,
 the first correction data is a correction data obtained from an error between the apparent diffusion coefficient measured in each position of the first phantoms and the known apparent diffusion coefficient, 
 the second correction data is a correction data obtained from an error between a spatial distribution of the measured apparent diffusion coefficient of the second phantom and the spatially uniform distribution of the known apparent diffusion coefficient of the second phantom, the error depending on spatial positions of the imaging region and having second or higher degree distribution function, and 
 said image generating unit corrects the second correction data so that the second correction data coincides with the first correction data at positions of the first phantoms, and generates the apparent diffusion coefficient image of the object corrected depending on the spatial positions using the corrected second correction data. 
 
     
     
       13. The magnetic resonance imaging system according to  claim 1 , wherein,
 the correction data is expressed as a ratio of the measured apparent diffusion coefficient and the known apparent diffusion coefficient. 
 
     
     
       14. The magnetic resonance imaging system according to  claim 1 , wherein,
 the correction data is expressed as a b value which is a parameter associating a signal strength S of diffusion weighted imaging data with an apparent diffusion coefficient ADC. 
 
     
     
       15. An RF coil unit, comprising:
 a phantom with a known apparent diffusion coefficient; 
 a receiving RF coil configured to receive magnetic resonance signal from an imaging object including said phantom and a object; and 
 a fixing unit configured to fix said phantom to said receiving RF coil. 
 
     
     
       16. The RF coil unit according to  claim 15 , wherein,
 said phantom has a size which covers a field of view. 
 
     
     
       17. The RF coil unit according to  claim 15 , wherein,
 said phantom is configured to have a plurality of phantom units. 
 
     
     
       18. The RF coil unit according to  claim 17 , wherein,
 each of said phantom units is arranged in the circumference of region for setting the imaging object inside said receiving RF coil. 
 
     
     
       19. The RF coil unit according to  claim 17 , wherein,
 said phantom unit is arranged in such position that a ghost artifact in a phase encoding direction does not occur. 
 
     
     
       20. The RF coil unit according to  claim 17 , wherein,
 each of the phantom units has the apparent diffusion coefficient of a value different from each other. 
 
     
     
       21. The RF coil unit according to  claim 17 , wherein,
 each of the phantom units is configured to have a plurality of subphantom units, each of the subphantom units having a known apparent diffusion coefficient of a value different from each other and being arranged in a substantially same position. 
 
     
     
       22. The RE coil unit according to  claim 17 , wherein,
 each of the phantom units has the known apparent diffusion coefficient of the same value, and number of the phantom units corresponds to degree of spatial distribution function of the measured apparent diffusion coefficient. 
 
     
     
       23. The RE coil unit according to  claim 15 , wherein,
 said phantom has an apparent diffusion coefficient close to an apparent diffusion coefficient of the object. 
 
     
     
       24. The RE coil unit according to  claim 15 , wherein,
 said phantom has a resonant frequency equivalent to a resonant frequency of water, 
 
     
     
       25. The RE coil unit according to  claim 17 , wherein,
 said phantom is formed in a pillar shape such that a longitudinal direction thereof corresponds to a direction of a body axis of the object. 
 
     
     
       26. The RE coil unit according to  claim 17 , wherein,
 said fixing means is configured to fix said phantom unit to a human body coordinate system. 
 
     
     
       27. The RF coil unit according to  claim 26 , further comprising:
 an antenna configured to wirelessly transmit a magnetic resonance signal received by said receiving RE coil. 
 
     
     
       28. An RE coil unit, comprising:
 a phantom with a known apparent diffusion coefficient; 
 a receiving RF coil configured to receive a magnetic resonance signal from an imaging object including said phantom and a object; and 
 a fixing unit configured to fix said phantom to a human body coordinate system.